Velvet worms immobilize their prey with slime fired out of their face cannons. "Well if you're going to act like that," says the little bug in the foreground, "I'm just going to leave." GIF: Nurie Mohamed/WIRED. Source: National Geographic

One of the animal kingdom’s more non-exclusive semantic clubs is that of the worms. Are you “any of a number of creeping or burrowing invertebrate animals with long, slender, soft bodies and no limbs,” as the New Oxford American Dictionary defines you? Well come on in—we have a seat just for you. From the ferocious (seriously) predatory marine bobbit worm to the horsehair worm, which invades crickets’ bodies and mind-controls them, it’s a club that’s as incredibly neat as it is diverse.

Hell, even if you have kinda-limbs we’ll consider letting you in. We’re looking at you, the more than 100 species of velvet worms, with your adorably stubby legs, face cannons that fire immobilizing slime, and nasty jaws that bore right through arthropod armor. You’re so ancient and unique and bizarre, so far removed from something like the average earthworm, that you get your very own phylum. But welcome to the club all the same.

The velvet worm may be velvety and squishy and tiny—between 0.5 and 6 inches long—but this critter is a ruthless hunter, not to mention quite the survivor. Velvet worms have been stalking Earth almost as long as land animals have existed. “They evolved during the Cambrian, approximately 540 million years ago, from a marine group called the lobopodians,” said biologist Ivo de Sena Oliveira of Germany’s University of Leipzig. “And despite their fragile aspect, velvet worms were able to overcome several geological, climatic, and vegetation changes until today.”

Velvet Underground

Perhaps that’s not surprising when you consider the weapons the velvet worm has at its disposal. On either side of its head are cannons—actually modified limbs—connected to a reservoir of slime made of proteins. In mere milliseconds, the worm can fire this goo at prey as far as 8 inches away, just like Spider-Man, only without the insufferable movie adaptations. The more its victim struggles to free itself from the slime, the more ensnared it becomes, like people watching Spider-Man movies.

In the worm’s mouth is a pair of jaws, each containing two blades that have a large sickle-like tooth and smaller teeth of the same shape. “The jaws of the velvet worms are actually modified limbs that move into the mouth during development,” said Oliveira. “And that is why the blades resemble the paired claws found in each leg. The musculature associated with the jaws is massive and complex and might have evolved to break the hard exoskeleton of their prey.”

Once their target is immobilized, “the velvet worms just walk slowly to the prey, make a small hole in its exoskeleton using the jaws, inject digestive saliva into its body,” and suck out the pre-digested tissues. And lest the slime go to waste, the worm eats that up as well. (Watch one hunt in the killer National Geographic video below.)

But how does the velvet worm find its prey in the first place? These are, according to Oliveira, absolute “sensorial machines.” Not only do they have eyes that likely provide them with monochromatic vision (a bit like seeing the world as an ’80s-era computer monitor, though probably not puke-green), but they also utilize their antennae to sniff out chemicals and changes in air currents. But most importantly, their entire body is covered with tiny bumps known as dermal papillae, which give the worm its velvety texture.

Most of these papillae have bristles that complement the antennae in processing air currents (you can tell species of velvet worm apart, by the way, by the shape of these bristles). Plus, the worms have another type of sensory structure spread all over their bellies, and “even though we do not know what kind of receptor each of these structures represents,” said Oliveira, “we can already speculate that these animals have a very good perception of the environment around them.”

Dermal Insemination, Hydrostatic Skeletons, and Other 10-Dollar Words to Get You to Keep Reading This Article

To watch a velvet worm amble around is quite hypnotic, as its many stubby legs ripple up and down its body. Like all manner of other invertebrates, the velvet worm has a hydrostatic skeleton that supports its body not with bone, but with pressurized fluid. (You may have noticed that when you kill a spider it’ll flip over and curl up its legs. That’s not for cartoonish effect—the critter is in fact losing its internal pressure). But what the worm can do with this system is unique.

Velvet worms go gaga for rotting logs, which provide them with moist habitats and maybe the occasional splinter. Martin Smith/Wikimedia

It can not only contract its body to fit through tight spaces, but “in a special situation, such as escaping from something, we usually say they ‘gallop,’” said Oliveira. That is, “the legs assume faster movements and at the same time they use the hydrostatic skeleton to contract and distend their bodies, doing a movement very similar but not as extreme as that of an inchworm. This is only possible because the hydrostatic pressure can be efficiently directed to any body parts using their developed body musculature.”

Now, when it comes to getting busy, the velvet worms have gotten downright creative with it during their half billion years of evolution—and why wouldn’t you, really. Males put off pheromones, a bit like wearing cologne, to attract the ladies. In most species, according to Oliveira, when the two come together they’ll mate by pairing their genital openings, with the male transferring a bundle of sperm called a spermatophore directly into the female’s body.

Other species take rather more bizarre approaches. Some Australian varieties, for instance, have “developed specialized head organs, with which the male can hold the spermatophore and put it into the female’s genital opening,” said Oliveira. And “males of some Chilean velvet worms lay spermatophores all over the female’s body, and the females are able to absorb them through the skin.” This is known as dermal insemination.

A velvet worm shows off its upcoming fall line of speckled formal wear. Hope you like velvet, because that’s what you’re gonna get. Bruno Vellutini/Wikimedia

Beyond the occasional roll in the hay, it’s been argued that velvet worms can even come together to form colonies. Ruled by a single female, the society is rigidly based on dominance and submission, with the queen always getting first dibs on a kill. But Oliveira argues that this is speculative, and that no one has yet proved it convincingly.

“I would rather associate such aggregations with environmental conditions,” he said, “as these animals naturally tend to concentrate in areas with optimal temperature and humidity conditions.” Velvet worms are quite susceptible to drying out, and must compete for space in rotting logs, which “are the only microhabitats that retain humidity and provide shelter for them and many other invertebrates during the dry season.”

So yeah, fine, perhaps we need to rethink social organization’s place in the velvet worm’s list of amazing qualities. But it still gets to stay in the worm club. Maybe we can make it secretary, or even treasurer, if that’ll help.

Browse the full Absurd Creature of the Week archive here. Have an animal you want me to write about? Email matthew_simon@wired.com or ping me on Twitter at @mrMattSimon.